The long-term goal of the proposed experiments is to identify the fundamental processing principles and strategies that underlie the cortical receptive field transformations and representations of complex sounds. We will contrast the organization of two primary auditory fields, Al and AAF, in adult cat with specific reference to functional domains and laminar organization. A main premise is that Al and AAF receive largely independent thalamic and cortical inputs and have specific functional differences that may constitute task- specific processing streams. How do the inputs differ in source location and functional properties;what do the thalamic inputs contribute to the generation of receptive field (RF) diversity;and how are the functional characteristics at the cortical input level transformed in the output layers? The interrelations between heterogeneous spatial distributions of functional properties and the connection patterns of these primary fields will be studied in joint electrophysiological and neuroanatomical experiments. By relating the functional properties and cortical connectivity, global principles underlying the characteristics of cortical representations and transformations can be assessed for simple and complex sounds. . The first aim is to define layer-specific functional organizations of Al and AAF for simple and complex sounds. We think that single neurons in layers Illb/IV will show systematic differences in RF attributes from cells in other layers. RFs will be obtained with traditional stimuli as well as with a reverse-correlation method that creates binaural spectro-temporal receptive fields. We will also compare the lamina-specific changes in RF properties in Al and AAF of the anesthetized cat and in A! of the awake squirrel monkey to address comparative questions and RF organization in conscious animals. The second aim is to compare directly the RFs of thalamic sources and cortical targets by simultaneous recording of functionally connected neuron pairs in cat medial geniculate body and AI/AAF. It is hypothesized that thalamic input properties approximate some RF properties of their cortical targets but that construction of many cortical RFs is substantially shaped by corticocortical contributions. Finally, we will relate thalamic and intracortical connections to functional sub-regions of Al and AAF. How patchy thalamic and corticocortical projections are related to the patchy cortical organizations found for spectral, temporal and binaural properties is the main question. Labeling from retrograde tracers injected into physiologically defined functional zones in cat AI/AAF will be assessed relative to functional maps. These studies will establish a functional and structural framework of signal processing in primary cortical fields. Insight into these principles is crucial for understanding the flow of information in auditory cortex, the circuits for normal auditory processing and perceptual learning, and their contributions to auditory disorders.